Golf clubs are generally grouped by type into woods, irons and putters. Putters are used primarily for striking the ball on the green. Irons generally provide varying loft from wedges to a one iron and are normally used for playing the ball from short distances with a higher degree of loft to intermediate distances up to about 200 yards. Wood style golf clubs are generally used for longer distance driving of the golf ball and may be fabricated of wood or metal such as stainless steel, aluminum or various alloys. Clubs of this latter type are generally termed or referred to by golfers as "woods" notwithstanding the particular material from which they are fabricated.
When using woods, as indicated above, the object is to drive the golf ball long distances along a desired flight path, usually straight, although in some cases a slight fade or hook is desired. To achieve optimum distance, it is important to strike the ball squarely on the hitting area or "sweet spot" of the club with the greatest possible club head speed which the golfer can achieve. Achieving the proper golf club speed is a matter of technique which must be learned often by arduous practice. Providing a solid impact area can be improved by the club design and materials. As indicated above, many current golf club designs rely on the use of improved materials for club heads and shafts such as metal alloys to improve the ball impact velocity to achieve a longer ball flight path. It is known, for example, to vary the weight distribution to improve the impact. Typical of such to designs are the well-known cavity and perimeter weighted club designs. It is also known to place metal plates in the face of wooden head clubs in the striking area to improve impact.
While these approaches have, to some degree, improved the golf club design and improved the ability of the user to strike the ball squarely, there nevertheless exists the need for improved golf clubs, particularly the wood type.
It is known that concentrating the mass in a wood style golf club at or behind the point of impact tends to increase the horizontal spin on the ball, thus tending to cause hooks and slices. This is believed to be caused by the club striking the ball somewhat off center. When an offset impact occurs and mass is concentrated behind the "sweet spot", a force is exerted which tends to rotate the club shaft about its axis so that the face is not perpendicular to the desired flight path. This imparts a slice or hook to the ball depending on the direction of spin. When the club head mass is concentrated in the extremity of the golf club rather than behind the "sweet spot", the moment of inertia is increased and there is more resistance to the club head rotation upon impact of the ball.
Another approach is to utilize various metal alloys in order to achieve light weight. Many of these clubs are hollow. If metallic clubs are solid, they often become too heavy for practical use. However, hollow club heads tend to provide a tinny sound upon impact which does not appeal to some golfers. Furthermore, if the face of a hollow club is too thin, it may deform upon impact affecting the golf shot.
Various patents relating to golf club heads having various structures within the golf club head can be found in the prior art including the following: U.S. Pat. Nos. 3,589,731; 4,655,458; 5,046,740; 4,461,481; 2,592,013; and 5,452,897. U.S. Pat. No. 5,586,948 discloses a golf club head with a metal sleeve filled with polyurethane.